We have studied acoustoelectric (AE) effect produced by surface acoustic waves (SAW) in a monolithic layered structure, composed of piezodielectric We show that the anomalous effect is caused by strong modulation of the film conductivity produced by the SAW elastic deformations.

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A rapid build-up of the off-axis thermal flux in an external electric field was shown in (I) to be an obstacle for the amplification of the longitudinal ultrasonic wave propagating along the X-axis in Te. The critical field E fication is about two times as large a s that for the off-axis thermal flux. Therefore the amplified flux produces the electric field redistribution and the ultrasound gain L for this mode ampli-C L C saturation when the drift field E is still less than E This is not the case for a slow shear wave (v = 1.48~10 cm/s) with wavevector . 5 S <\I? a s the critical drift fields for the wave and the off-axis thermal flux are close.It is for this mode that about 35 dB/cm (2, 3) ultrasonic gain has been observed at the frequency of 45 MHzthe largest gain known before for Te.if one comes to higher frequencies (the linear theory predicts a f2 dependence). Furthermore these measurements allow to determine the piezoelectric constant e whose value i s not known definitely (Table 1).It was interesting to find out how much the real gain for that orientation increases 11 The sound amplification measurements for the chosen geometry are complicated because of the strong inclination (at an angle of about 46 30' in Te) of the sound beam direction with respect to the wavevector. In practice, only measurements with a single transducer (reflection method) on comparatively short samples are possible.The samples were obtained by cleavage at 77 K. 0In this paper we report experimental results which were obtained when measuring the slow shear Y-wave amplification in Te in the frequency range 116 to 220 MHz at 77 OK. 0 14 -3 The carrier density and mobility of holes at 77 K were (1.9 to 3 . 9~1 0 )cm and (1.6 to 3 . 7~1 0 ) cm /Vs, respectively, The sample length varied from 2.1 to 3.9 mm. 2Quartz or lithium niobate transducers were used for sound excitation. The input

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